Malondialdehyde (MDA) is found in the modest amounts in meat and some other foods. Early reports implicated MDA as a mutagen and a carcinogen. The objective of this investigation is to determine through well controlled chronic studies if MDA is carcinogenic if it is taken internally. Most of the previous work was conducted with the product of the acid hydrolysis of tetramethoxypropane. We estimate the yield of this reaction to be 30-40% with many contaminating species. We prepared greater than 95% pure MDA and have used it in eye irritation tests, mouse skin painting tests, acute intraperitoneal toxicity tests, and 90-day subchronic oral toxicity tests. We find the purified preparation to be much less toxic than previously reported with no indicattion of carcinogenicity at this point. We have further purified sodium MDA to greater than 99% purity and are currently testing it for mutagenicity in the Ames salmonella revertant assay. We will soon initiate chronic oral exposures as a final assay for carcinogenicity.